Epithelial cells of the attached gingiva of mice are being isolated and cultured. The effect of various exogenous and endogenous toxins on these culture cells will be evaluated for their possible role in periodontal disease. Experiments are in progress to determine the antigenicity of epithelial explants in syngeneic and allogeneic mice. The graft rejection phenomenae will be evaluated for explants which have been maintained in tissue culture for varying time periods.